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Mixed effects model- can I get SPSS to recognise a fixed factor as a continuous variable

  • 1.  Mixed effects model- can I get SPSS to recognise a fixed factor as a continuous variable

    Posted Thu May 06, 2021 10:53 AM
    Would appreciate any advice/knowledge. I am trying to run a mixed effects model with time as a continuous variable. I am interested in a group/time interaction so want to put group and time as fixed factors, plus to include the interacting term group * time.

    However, when I run the model, although Time is set as a scale variable, the mixed model seems to set each time point as a separate non-continuous time point and makes interpretation of the Estimates of Fixed effects very difficult because it is giving me a fixed effect estimate for every time point in the model.

    Is there a way of forcing SPSS to recognise a variable as a fixed effect as a continuous variable ? There seems to be no option for this. I see in STATA you can define a fixed factor as continuous by simply prefixing it as "c.".

    any advice appreciated ( I may have to learn STATA to do this if no other way).

    thanks

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    Enric Vilar
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    #SPSSStatistics


  • 2.  RE: Mixed effects model- can I get SPSS to recognise a fixed factor as a continuous variable

    IBM Champion
    Posted Thu May 06, 2021 04:22 PM
    If you are using GENLINMIXED,

    from the CSR
    "The FIXED subcommand specifies a main effects model with fields .... If they are
    continuous, they will be treated as covariates, if categorical, they will be treated as factors."

    So set the measurement level appropriately in the Data Editor Variable View or with the VARIABLE LEVEL command.

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    Original Message


  • 3.  RE: Mixed effects model- can I get SPSS to recognise a fixed factor as a continuous variable

    IBM Champion
    Posted Thu May 06, 2021 04:27 PM
    And ...

    FIXED Subcommand
    The FIXED subcommand is used to specify fixed model effects, including the intercept.
    • This subcommand is optional. If not specified, then the procedure builds an intercept-only model.
    EFFECTS. The effect list includes all effects to be included in the fixed model except for the intercept,
    which is specified using the USE_INTERCEPT keyword.
    • To include a term for the main effect of a factor (categorical predictor) or covariate (continuous predictor), enter its field name. Whether a field is treated as a factor or covariate depends upon its measurement level. Fields with categorical (flag, nominal, or ordinal) measurement level
    are treated as factors while fields with continuous (scale) measurement level are treated as covariates.


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    Original Message